Semiconductor integrated circuit device

Abstract: Protection lines (14, 17) are arranged on both sides of and above a signal line (13), and ground lines (15) are formed outside the protection lines (14) and a ground line (19) is formed above the protection line (17). A bias circuit (21) is connected to the signal line (13) and protection lines (14, 17) to set the potential of the protection lines (14, 17) equal to that of the signal line (13) and set the impedance of the protection lines low. The signal line (13) processing a small signal, is surrounded by the low-impedance protection lines (14, 17) of the same potential as that of the signal line (13), and thus crosstalk can be prevented from occurring between the lines, without causing the components of a high-frequency analog signal to attenuate.

Description: The present invention relates to a semiconductor integrated circuit device and, more specifically, to an integrated circuit (IC) including an analog circuit and a digital circuit together. In a conventional integrated circuit (IC) including both an analog circuit and a digital circuit, a digital signal having a large amplitude and an analog signal having a small amplitude are processed on the single IC. It is thus necessary to prevent the digital signal from leaking into the analog signal. For example, the leakage of a signal through a substrate can be prevented by acquiring a substrate potential from each of analog and digital circuits or by forming a number of substrate contacts. In the above integrated circuit, the wiring length is increased in accordance with a reduction in wiring interval and an improvement in degree of integration of IC; accordingly, a crosstalk is caused between wirings owing to a signal leakage therebetween. To prevent the crosstalk, as shown in FIG. 1, a ground (GND) line 5 is formed above wiring 3, which is formed on an insulation film 2 on the major surface of a substrate 1 and serves as a signal line, with an insulation film 4 interposed between the wiring 3 and GND line 5. The wiring (signal line) 3 is therefore covered with the GND line 5. However, in the conventional integrated circuit described above, the parasitic capacitance between the wiring 3 and GND line 5 is increased when the wiring 3 is long or wide. Since the resistance of a high-frequency analog signal is usually represented by 1/jωC (ω : radian frequency, C : capacitance), the components of the high-frequency analog signal attenuate as the capacitance increases. Furthermore, the potential of the signal is likely to change because of a leak of small current flowing between wirings. As described above, the conventional integrated circuit has a drawback in which when the wiring layer is covered with the GN line to prevent a crosstalk from occurring between the wires, the components of the high-frequency analog signal may attenuate or the potential of the signal may change. The European Patent Application EP 0 536 972 A2 discloses an integrated circuit device having an improved substrate capacitance and isolation. On a substrate a first insulation film made of SiO 2 , a first metal layer, a second insulation film made of SiO 2 and a second metal layer are formed in the stated order. The second metal layer is selectively etched to constitute a first wiring including a bonding pad on the edge of the structure and connected thereto trace runs. The first metal layer is also selectively etched to comprise a second wiring including a bonding pad and trace runs corresponding to those selectively formed in the second metal layer. The trace runs are interrupted by an operational amplifier constituted by a high impedance unity gain voltage amplifier. The input of the operational amplifier is connected to a trace run of the first wiring and the output of the operational amplifier is connected to another portion of a trace run and to the bonding pad of the second wiring. The European patent application EP 0 181 600 A1 describes that a transmission line wiring and an auxiliary line are formed parallely. Between one of the transmission lines and the end of the auxiliary line a wave shaping circuit is provided which consists of two serially connected inverters. Thus, the output end of the auxiliary line floats electrically. The European patent application EO 0 353 426 A2 discloses that signal interference prevention wirings may be disposed between two wirings which are arranged in parallel for transmitting a signal. The signal interference prevention wiring is held at a constant potential. It is accordingly an object of the present invention to provide a semiconductor integrated circuit device capable of providing both a digital circuit and a high-precision analog circuit together on a single device, and preventing a digital signal from leaking into an analog signal without attenuating the components of a high-frequency analog signal or changing the potential of the signal. This object is solved by a semiconductor integrated circuit device according to claim 1. Further advantageous embodiment, and improvements of the invention are listed from the dependent claims. With the claimed circuit arrangement, even though the signal line processing a small signal is lengthened, it can be protected from any influence of the other lines. Therefore, noise generated from the other lines can be suppressed, as can be crosstalk between the signal line and the other lines. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a cross-sectional view of a conventional semiconductor integrated circuit; FIG. 2 is a cross-sectional view of a semiconductor integrated circuit according to an embodiment of the present invention; FIG. 3 is an equivalent circuit diagram of the semiconductor integrated circuit shown in FIG. 2; and FIGS. 4 to 12 are cross-sectional views each showing other semiconductor integrated circuits wherein Figs. 6, 9, 10, 11, 12 show other embodiments of the present invention and wherein Figs. 4, 5, 7, 8 show other aspects which may be used in the embodiments of the invention. An embodiment of the present invention will now be described, with reference to the accompanying drawings. FIG. 2 shows a constitution of an integrated circuit (IC) according to an embodiment of the present invention, and FIG. 3 shows an equivalent circuit of the IC of FIG. 2. As illustrated in FIG. 2, the IC includes a semiconductor substrate 11 on which, for example, a digital circuit and an analog circuit, neither of which is shown, are formed, an insulation film 12 formed on the major surface of the substrate 11, a signal line 13 of first wiring formed on the film 12, protection lines 14 of second wirings formed on both sides of the signal line 13, ground lines 15 of third wirings formed outside the lines 14, a protection line 17 of fourth wiring provided above at least the signal line 13 with an interlayer insulation film 16 between them, a ground line 19 of fifth wiring formed above the line 17 with an interlayer insulation film 18 between them, and a surface protection film 20 formed on the line 29. To improve in protection effect, it is preferable that the fourth wiring 17 extends over the second wirings 14 as well as the first wiring 13 so as to cover the second wirings, as shown in FIG. 2. As illustrated in FIG. 3, a bias circuit 21 is connected to the signal line 13 and protection lines 14 and 17 to set the potential of each of the lines 14 and 17 equal to that of the line 13. The bias circuit 21, which is constituted of a voltage follower amplifier, enhances an impedance between the signal line 13 and the protection lines 14 and 17, and supplies the same potential as that of the signal line 13 to the protection lines 14 and 17 at a low impedance. As shown in FIG. 3, the protection lines 14 and 17 are connected to one input terminal and an output terminal of the amplifier 21, whereas the signal line 13 is connected to the other input terminal thereof. For simplification of the drawings, in FIG. 2 and its subsequent Figures of cross-sectional views, the connection lines of the protection lines 14 and 17 to the bias circuit 21 are schematically shown, but the connection line between the signal line 13 and bias circuit 21 is not shown. A method of manufacturing the above-described integrated circuit in Fig. 2 will now be described. First an analog circuit and a digital circuit (neither is shown) are formed on a semiconductor substrate 11. Then an insulation film 12 is formed through a normal process, e.g., a CVD method. A contact (not shown) is formed in the insulation film 12 through the PEP (photo engraving process), and aluminum is deposited by sputtering. After that, the aluminum is patterned to form the signal line 13, protection lines 14, and ground lines 15. The protection lines 14 are arranged on both sides of the signal line 13 such that they are parallel with the line 13, and the ground lines 15 are formed outside and in parallel with the protection lines 14. The signal line 13 and protection lines 14 are connected to the bias circuit 21, and the ground lines 15 are connected to their respective grounds. An interlayer insulation film 16 is formed by the CVD and a through hole (not shown) is formed by the PEP, with the result that the protection line 17 is formed on the interlayer insulation film 16 in the same manner as the protection lines 14 are formed. The protection line 17 connected to the bias circuit 21, is provided above the signal line 13 and covers it and, in other words, the protection line 17 is formed so as to cover the signal line 13, though the interlayer insulation film 16 is interposed between the lines 13 and 17. To improve the protection effect, it is preferable to extend the protection line 17 over the protection lines 14 as well as the signal line 13, so as to cover the protection lines 14. Similarly, an interlayer insulation film 18 is deposited by the CVD and a through hole (not shown) is formed by the PEP or the like. After that, a ground line 19 is formed on the interlayer insulation film 18 and connected to the GND. The ground line 19 is formed so as to cover the protection line 17. More specifically, the ground line 19 is formed above the protection line 17 so as to cover the line 17 in the thickness direction of the substrate 11, though the interlayer insulation film is interposed between the protection line 17 and ground line 19. After that, a surface protection film 20 for protecting the surface of the resultant structure is deposited by sputtering or the like, and a pad (not shown) is formed, thus completing the integrated circuit. In the foregoing integrated circuit as shown in Fig. 2, the signal line 13, which processes a small signal, is surrounded by the low-impedance protection lines 14 and 17 having the same potential as that of the line 13 and by the ground lines 15 and 19 connected to the GND. Therefore, no crosstalk can be prevented from being caused between the signal line 13 and the protection lines 14 and 17. Since the interconnection between the protection lines 14 and 17 and the other lines (not shown) is protected by the ground lines 15 and 19, crosstalk is difficult to cause between them. Since, moreover, the protection lines 14 and 17 are low in impedance, they are not influenced greatly by the parasitic capacitance or the leak of small current, with the result that the great influence can be prevented from being exercised on the signal line 13. Consequently, the integrated circuit of the present invention as shown in Fig. 2 overcomes the problems of the conventional circuit in which the parasitic capacitance between the signal and ground lines is increased, the components of a high-frequency analog signal is attenuated, and the potential of the signal is varied with the leak of a small current between wirings. In the above embodiment, since the signal line processing a small signal is surrounded by the low-impedance protection lines of the same potential as that of the signal line, the parasitic capacitance between the signal line and ground lines can be prevented from increasing, and noise generated from the other wirings can be suppressed, as can be crosstalk between the signal line and the other wirings. Consequently, the signal line can be protected irrespective of the length or area thereof and, even when both a digital circuit and a high-precision analog circuit are integrated on a single device, the performance of the device itself can be sufficiently maintained. In the above embodiment of the invention, each wiring is constituted of aluminum. However, the present invention is not limited to this, but the first and second wiring can be constituted of polysilicon, polycide, or the like. In the above embodiment, the first wiring serves as a signal line, and the protection lines are formed above and on both sides of the signal line. Some aspects of the embodiment as shown in Fig. 2 are separately shown and discussed with respect to Figs. 4 and 5. As shown in FIGS. 4 and 5, however, a protection line or protection lines can in principle be formed either on both sides or above the signal line. The integrated circuit of the present invention includes at least the first wiring 13 of the signal line and the protection lines 14 and protection line 17. Fig. 6 shows the basic embodiment of the invention, Fig. 7 and Fig. 8 explain some aspects of the invention usable with the embodiment in Fig. 6 and Figs. 9, 10, 11, 12 show other embodiments based on Fig. 6. FIG. 6 shows an integrated circuit comprising both the protection lines 14 and 17. FIG. 7 shows an integrated circuit including protection lines 14 and ground lines 15 outside the lines 14. FIG. 8 illustrates an integrated circuit having a protection line 17 and a ground line 19 above the line 17. FIG. 9 shows an integrated circuit including both protection lines 14 and 17 and ground lines 15 outside the lines 14. FIG. 10 illustrates an integrated circuit comprising protection lines 14 and 17 and ground lines 15 and 19. The integrated circuit of the embodiments in Fig. 2 and Fig. 10 has a three-layered wiring structure, and the signal line is the lowest layer of the structure. On the other hand, as shown in FIGS. 11 and 12, the number of wiring layers can be four or more, and a protection line can be formed under and alongside the signal line. Furthermore, a ground line can be formed for the protection line. In FIG. 11, a protection line 27 is formed under a signal line 13 with an insulation film 26 interposed between them. The protection line 27 is formed so as to cover the signal line 13 and preferably extends so as to cover protection lines 14. In FIG. 12, a ground line 29 is provided under a protection line 27 with an insulation film 28 interposed between them. The protection effect of the circuits shown in FIGS. 11 and 12 is improved more greatly than that of the circuit shown in FIG. 2. According to the foregoing embodiments, the signal line and protection lines are interposed between the ground lines. However, as shown in FIGS. 4, 5 and 6, the ground lines need not be always provided. In the aspects of the embodiments shown in FIGS. 4, 5, 7 and 9 and the embodiment in Fig. 6 the insulation film 18 is used as a surface protection film. In the aspects of the embodiments shown in FIGS. 4 and 7, the insulation film 18 need not necessary be formed when the insulation film 16 is used as a surface protection film. It is needless to say that various changes and modifications can be made without departing from the scope of the subject matter of the present invention as defined in claims and in accordance with Art. 69 of the EPC protocol. According to the above-described semiconductor integrated circuit device of the present invention, a digital circuit and a high-precision analog circuit can be formed together on a single device, and a digital signal can be prevented from leaking into an analog signal, without attenuating the components of a high-frequency analog signal or varying the potential of the signal.

Claims: A semiconductor integrated circuit device comprising: a) a semiconductor substrate (11); b) a first wiring layer including a signal line (13) provided in a second insulation film (16) formed on a first insulation film (12) arranged on a major surface of said semiconductor substrate (11); c) a second wiring layer (14, 17, 27) formed in said second insulation film (16) adjacent to said signal line (13) separated therefrom by parts of said second insulation film (16); and d1) a bias circuit (21) constituted by a voltage follower amplifier (21) for setting a potential of said second wiring layer (14, 17, 27) equal to that of said adjacent signal line (13); wherein d2) said bias circuit (21) is a voltage follower amplifier (21) having one input terminal connected to an output terminal thereof, receiving said potential of said signal line (13) at another input terminal at a high impedance and supplying a signal of the same potential but of a low impedance to said second wiring layer (14, 17, 27); wherein e1) said second wiring layer (14, 17, 27) comprises a first and second protection line (14) arranged on opposite sides of the signal line (13), substantially parallel to said signal line (13), and e2) said second wiring layer (14, 17, 27, Fig. 6) further comprises a third protection line (17) formed in a third insulation film (18) arranged on said second insulation film (16), said third protection lines (17) extending over said signal line (13) and said first and second protection lines (14) and being separated therefrom by parts of said second insulation film (16). A semiconductor integrated device (Fig. 11, 12) according to claim 1, characterized in that said second wiring layer (14, 17, 27) further comprises a fourth protection line (27) formed in a fourth insulation film (26) arranged between said first and second insulation films (12, 16), said fourth protection line (27) extending over said signal line (13) and said first and second protection lines (14) and being separated therefrom by parts of said fourth insulation film (26). A semiconductor integrated device (Fig. 7, 9) according to claim 1 or 2, characterized by a third wiring layer (15, 19, 29) comprising a first and second ground line (15) respectively arranged on a side of said first and second protection lines (14) not facing said signal line (13) in said second insulation layer (16) and being separated therefrom by parts of said second insulation film (16). A semiconductor integrated device (Fig. 2, 10) according to claim 1 or 3, characterized in that a third ground line (19) is provided in a fifth insulation film (20) arranged on said third insulation film (18), separated from said third protection line (17) by parts of said third insulation film (18) and covering same in the thickness direction. A semiconductor integrated device (Fig. 12) according to claim 4 and 2, characterized by a fourth ground line (29) formed in a sixth insulation layer (28) arranged between said first and fourth insulation films (12, 26) separated from said fourth protection line (27) by parts of said sixth insulation film (28) and covering same in the thickness direction.

Inventors: ITO TAKAO, ITO, TAKAO, ITO, TAKAO, C/O INTELLECTUAL PROPERTY DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1994
Main classification: H01L23
IPC codes: H01L23, H01L21